So I have an s5, and swapped a s4 waterpump housing... so its all s5 with an s4 pump.. now Ive been having noisey alt belts since then and just now looked up that the s4 and s5 water pump pulleys are different. *fromt what i see on mazdatrixs site so im just assuming that* Could that be the cause of my noisey belts? SHould i look for a S4 water pump pulley?

 

guess i found my answer, s5 pulley has a larger hole so it wont be hubcentric on the s4 pump.. ill check mine out and see if that could be why.

 

I have an s4 and the center rod for the water pump is 17mm.

When I ordered the gilmer pulley set from rotary works, they sent me a 15mm water pump pulley. So I have no definitive answer yet as to what came with what. I would just measure the center dowel/rod on the water pump, and the whole on the pulley your loOking to get.

 

Rotary-Works would have either sent you a 15mm or a 17mm ALTERNATOR Pulley,as they differ from S4 to S6.
Good luck getting that kit to 'fit like a glove".HINT: the belt is TOO Small!..(for an FC with an FD alternator)...and they don't care.
OP: I'm not sure about pulley size in the waterpump itself.You would think they would be.
If you are having Belt squeak,I would Clean the V groove on the pulley to see if that helps.
IF you go ahead and DO find out that the Pulleys are Indeed different,Please PM me,as I like knowing Info like that.it comes in Useful down the road.
OH!.Have you checked the alignment of the Pulleys to see if the alternator is Off a Bit?.I found that IF the alternator Main Bolt(the BIG long one) is loose,then it can cause Belt squeak and alternator Vibration.I just about lost my Head on that one!!!!